It is desirable to detect and quantify in foods and agricultural products analytes that may be indicative of the freshness or quality of the food. In routine quality control testing of foods, it is common practice to test for the presence of various contaminants, additives, degradation products, and chemical markers of microbial infestation, e.g., bacteria, bacterial endotoxins, mycotoxins, and the like. However, current methods by which such quality control testing is accomplished are typically either complex and skill-intensive analytical chemistry procedures or highly subjective and qualitative sensory evaluations, e.g., smell test, taste test, appearance, etc.
Furthermore, despite improvements in agriculture and food processing, outbreaks of disease from water-borne and food-borne pathogens still occur, including bacterial water- and food-borne diseases caused by Clostridium botulinum (botulism); Clostridium perfringens (food poisoning); Staphylococcus aureus (food poisoning); Streptococcus species (gastroenteritis); enteropathogenic Escherichia coli (gastroenteritis); Shigella dysenteriae (dysentery); Salmonella species (gastroenteritis); and Vibrio cholerae (cholera). There are also numerous water- and food-borne protozoan pathogens, such as Entamoeba histolytica, Giardia lamblia, Cryptosporidium, Microsporidia, and Cyclospora. In an attempt to avoid disease, food and water is often sampled and tested prior to distribution to determine whether it is contaminated by pathogenic microorganisms.
Numerous testing methods are available, but the following steps (or similar steps) are common to many methods: First, a pre-enrichment step is performed on a specimen to increase the number of pathogenic organisms present. The organisms are cultured in a non-selective growth medium typically for 24 hours or more. Pre-enrichment is usually necessary because pathogenic organisms may be present in very dilute amounts, thus making them difficult to detect. Second, an enrichment step may be performed in which a portion of the culture medium is transferred to an enrichment medium containing inhibitors that select for a pathogen of interest. The selected pathogen will grow further while other organisms are inhibited. Third, a measurement step is performed to discern whether pathogens of interest are present. Generally, a portion of the enrichment medium is streaked onto selective or differential agar media. The media will contain inhibitors effective against most organisms except the pathogen of interest. Indicator compounds (e.g. dyes) allow pathogen types to be visibly differentiated and thus indicate the presence and number of pathogens of interest. Exemplary alternative measurement steps are radioimmunoassay (RIA) tests, immunofluorescent assay (IFA) tests, enzyme immunoassay (EIA or ELISA) tests, DNA methods (e.g., PCR), and phage methods. Such methods are disadvantageous because they postpone distribution of fresh foodstuffs while specimens are culturing, particularly where freshness or spoilage concerns are present or it is otherwise impractical to store the food for extended periods. Furthermore, conventional methods typically only assay a small portion of an agricultural crop (≦250 g), which may lead to analytical results that are not representative of a harvested crop as a whole.
A need exists for a convenient rapid, cost-effective, and reliable method for testing for the presence of pathogens or infectious microorganisms in vegetables, fruits, nuts and other plant material intended, e.g., for animal or human consumption.